Here's an Olympic factoid that surprised me: there are about 700 athletes in London with confirmed asthma diagnoses, and (if trends from past Olympics continue) those athletes will be roughly twice as likely to win a medal as their non-asthmatic peers.

This “asthmatic advantage” was once thought to result from the performance-enhancing effect of asthma drugs. But recent research at the University of British Columbia and elsewhere has debunked this theory, shedding light instead on the link between intense exercise and respiratory function, and on the crucial role of a good warm-up for managing exercise-induced asthma without drugs.

That's an excerpt from my column in this week's Globe and Mail, which looks at the complicated relationship between asthma, asthma drugs, and sports performance. The most practical piece of information: a proper warm-up can make a big difference in whether you run into respiratory trouble during exercise:

It turns out that asthma attacks produce a “refractory period,” during which the airways become temporarily immune from a further attack. As a result, a warm-up that is sufficiently long and intense to sensitize the airways may allow athletes to get through their competition or time trial without suffering an attack.Most elite athletes already do this kind of warm-up as a matter of course, but others can benefit too. “With a better warm-up, you can get away with less drugs,” Dr. Koehle says.

As for the origins of the mysterious "asthmatic advantage," the leading theory is that prolonged training, particularly in certain endurance sports, can eventually damage the airways. As a result, the athletes with asthma are generally the ones who've been training longest and hardest -- and thus, are more likely to medal. For example, 17 percent of cyclists and 19 percent of swimmers in Beijing reported asthma diagnoses; those athletes won 29 and 33 percent of the medals in those sports, respectively.More data, from a paper published in the Clinical Journal of Sports Medicine last year: